Hadronic matter near the boiling point

Hadron collisions above ∼10 GeV/c primary laboratory momentum show an interesting global aspect (i.e. when averaged over all final channels): they can be described as a superposition of a rather special form of thermodynamics and of the kinematics of collective motions in the forward-backward direction. The thermodynamical behaviour is similar to that of boiling; the boiling temperatureT0 is not exactly known but near to 160 MeV; its value and the whole thermodynamic behaviour of hadronic matter follow uniquely from the hadronic mass spectrum. Namely, in this model, as a consequence of a kind of asymptotic bootstrap involving all hadrons, the mass spectrum of hadrons turns out to grow necessarily like exp [m/T0] whereT0 is the highest possible temperature (boiling point of hadronic matter). Global aspects of hadron collisions from ∼10 GeV/c up to the highest cosmic-ray primary momenta (>105 GeV/c) namely: production rates, differential momentum spectra of secondaries, transverse-momentum distributions, etc., agree well with the calculations based on this model. The known part of the hadronic mass spectrum does indeed grow exponentially and the mean transverse momenta of pions produced between 10 and 105 GeV/c primary momentum correspond toT≈120 to 160 MeV. The following speculative picture emerges: these seems to exist a highest temperature (or boiling point of hadronic matter)T0≈160 MeV; hadronic matter in collisions above some ten GeV/c primary momentum is in a state whereall hadrons melt by way of a universal hadronic bootstrap, into «boiling hadronic matter» in which strong collective motions in the direction of the collision axis coexist with local thermodynamical equilibrium.

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